An non-aqueous electrolyte secondary battery (hereinafter, also referred to as secondary battery) including representatively a lithium ion secondary battery is widely used in consumer devices because of their high capacity, high energy density and excellent storage performance and charge and discharge repeating characteristics. On the other hand, an adequate safety measure is required because a secondary battery uses lithium metal and a non-aqueous electrolyte.
For example, when a short circuit occurs between a positive electrode and a negative electrode due to some reason in a secondary battery having a large capacity and high energy density, an excess short circuit current flows. Since the short circuit current makes an internal resistance to generate Joule heat, the temperature of the secondary battery also rises. The secondary battery with increased temperature can go into an abnormal condition. For this reason, the secondary battery using a non-aqueous electrolyte including the lithium ion secondary battery is provided with a function of preventing themselves from going into an abnormal condition.
Among a number of proposals for a function of preventing an abnormal condition that have been made heretofore, there is a proposal described in Japanese Unexamined Patent Publication No. HEI 11 (1999)-102711 (Patent Document 1). This proposal reports a lithium ion secondary battery wherein for a collector composed of a resin film having a low melting point (130° C. to 170° C.) and metal layers formed on both faces of the same, a positive electrode and a negative electrode formed with active material layers of a positive electrode and a negative electrode are used.
In the secondary battery having the collector containing a resin film, when abnormal heat generation occurs due to a short circuit, caused by contamination of foreign matters between the positive electrode and the negative electrode, for example, the resin film having a low melting point fuses and the metal layer formed on the top thereof is also broken. Due to such fusion and breakage, the current between the positive electrode and the negative electrode is cut. It is believed that as a result of this, the temperature rise inside the secondary battery is suppressed and ignition is prevented.